1. Field of the Invention
This invention relates generally to a miniature motor, and more specifically to a miniature motor having a rotor constructed so as to enable the angular positioning of a commutator and a rotor core by engaging locating projections provided on the commutator with locating key holes provided on the rotor core, in which the locating projections are engaged with the locating key holes in two steps to enable to automate the winding of rotor windings, the connection of the ends of the rotor windings to the commutator tongues, and the mounting of the commutator on the rotor.
2. DESCRIPTION OF THE PRIOR ART
In miniature motors having brushes and a commutator, in which power is fed to rotor windings via the brushes and the commutator, the relative angular positions of the rotor core and the commutator are usually predetermined. In such a miniature motor, therefore, locating projections 2 are provided on a commutator 1, as shown in FIGS. 3 (A) and (B), and locating key holes (hereinafter referred to as key holes) 4 for engaging with the locating projections (hereinafter referred to as projections) 2 are provided on a rotor core 3, as shown in FIG. 3 (C); the projections 2 being engaged with the key holes 4 to accurately position the commutator 1 with respect to the rotor core 3. FIGS. 3 (A) and (B) are front and bottom views of the commutator, FIGS. 3 (C) and (D) are plan and side views of the rotor core, and FIGS. 3 (E) and (F) are front views of the rotor, respectively. In the figure, reference numerals 1 refers to a commutator; 2 to a projection; 3 to a rotor core; 4 to a key hole; 5 to a commutator segment; 6 to a commutator tongue; 7 to a rotor shaft; 8 to a rotor; 9 to a rotor winding; 10 to a winding end; and 11 to a commutator reference surface; 13 to a column made of an insulating material; 14 to an enlarged portion, made of an insulating material; and 15 to a washer, respectively.
When winding the rotor winding 9 on the rotor core, as shown in FIG. 3 (E), is is desirable, in terms of improved productivity in the manufacture of the rotor, to wind the rotor winding 9 on the rotor core 3 in a state where the commutator 1 is mounted in advance on the rotor 8, so that the winding end 10 can be temporarily attached to the commutator tongue 6 during the aforementioned winding operation. In order to make it possible to include the operation of attaching the winding end 10 to the commutator tongue 6 during the winding operation, the commutator tongue 6 must be located at a position higher than the height of the winding (shown by an arrow H), as shown in FIG. 3 (E). To achieve this, the length (shown by an arrow L.sub.2 in FIG. 3 (A)) of a commutator portion below the enlarged portion 14 is made larger than the winding height H.
With the increased need for thinner miniature motors in recent years, however, various means for making the rotor thinner have been conceived. As one of such means, it has been conceived that the commutator segment length (shown by an arrow L.sub.1) and the aforementioned length L.sub.2 of the commutator 1 shown in FIG. 3 (E) are reduced to the minimum. If the length L.sub.2 is reduced, however, the position of the commutator tongue 6 tends to be lower than the winding height H, as shown in FIG. 3 (F), posing difficulties in the abovementioned winding operation. To overcome this problem, the winding operation is usually performed in the following three methods.
(i) As shown in FIG. 3 (E), the commutator 1 is pressfitted to the rotor shaft 7 until the commutator tongue 6 reaches a position higher than the winding height H, and then the projections 2, 2 and 2 (shown in FIG. 3 (A)) are positioned almost above the key holes 4, 4 and 4 (shown in FIG. 3 (C))(at this time each projection 2 has not yet been inserted into each key hole 4). In this state, the winding operation, including the operation of attaching the winding end 10 to the commutator tongue 6, is performed. After the winding operation is completed, the commutator 1 is forced toward the rotor core 3 and each projection 2 is inserted into each key hole 4 until the commutator reference surface 11 (shown in FIG. 3 (A)) comes in contact with the rotor core 3.
(ii) After the rotor winding is wound on the rotor core 3, the commutator 1 is fitted to the rotor, and then the winding end 10 is connected to the commutator tongue 6.
(iii) Though not shown in the figures, a locating knurled portion is provided on the rotor shaft, instead of the projections 2 and the key holes 4. The rotor winding and commutator fitting operations are similar to those in (i) above.
In the foregoing, the rotor winding and commutator fitting operations for the conventional miniature motors have been described. These methods, however, have the following unwanted problems.
In the method (i), when mounting the commutator 1 on the rotor after the rotor winding operation, merely pushing the commutator 1 toward the rotor core 3 may result in a mismatching between the projections 2 and the key holes 4. The commutator 1 must therefore be forced toward the rotor core 3, while adjusting the relative positions of the projections 2 and the key holes 3. This tends to deteriorate working efficiency.
In the method (ii), the rotor winding operation is performed independently of the operation of attaching the winding end 10 to the commutator tongue 6. This not only deteriorates working efficiency but also makes it difficult to position the projections 2 and the key holes 4, as in the case of the method (i).
Furthermore, in the method (iii), an additional knurling operation is required, increasing the manufacturing manhours.